1. Field of the Invention
The invention relates generally to gate valves for controlling fluid flow. More particularly, the invention relates to sealing assemblies for gate valves.
2. Background of the Technology
In general, a valve is a device that controls fluid flow through a conduit. A gate valve or sluice valve is a particular type of valve that opens by lifting a round or rectangular gate out of the path of the fluid. Gate valves typically include a valve body including a fluid flow passageway, a gate chamber perpendicular to the fluid flow passageway, and a gate slidably disposed in the gate chamber. A bonnet is secured to the top of the valve body and closes off the gate chamber from the external environment. The gate is moveable within the gate chamber between a “closed” position in which gate extends across the fluid flow passageway and obstructs the flow of fluid through the valve, and an “opened” position in which the gate does not obstruct the flow of fluid through the valve. A stem extending through the bonnet and into the gate chamber is coupled to the gate and used to externally control the position of the gate (i.e., to open and close the gate).
Most gate valves also include an upstream and a downstream valve seat, each disposed in the fluid flow passageway and extending between the valve body and the gate. In particular, the valves seats allow fluid flow through the valve, but function to restrict fluid communication between the gate chamber and the fluid flow passageway.
Typically, when the valve is closed, either the upstream valve seat functions to isolate the gate chamber from the fluid flow passageway, or the downstream valve seat functions to isolate the gate chamber from the fluid flow passageway, but not both simultaneously. For upstream sealing valve seats, the fluid in the passageway upstream of the closed gate is prevented from reaching the gate chamber. This provides the advantage of limiting potentially corrosive fluids in the closed valve upstream of the gate from reaching the gate chamber. Further, by preventing such corrosive fluids from entering the gate chamber, risks to maintenance and service personnel that may need to periodically close and access the gate valve are reduced. However, a phenomena referred to as the “double blocking effect” often arises in upstream sealing valve seats. The double blocking effect occurs when both the upstream and downstream valve seat are compressed against the gate, thereby making the gate difficult to move within the gate chamber to transition the valve between the closed and open positions.
On the other hand, for downstream sealing valve seats, the fluid in the passageway upstream of the closed gate is allowed to reach the gate chamber, however, the downstream valve seat prevents the fluid in the gate chamber from reaching the portion of the fluid passageway downstream of the gate. This design tends to reduce or eliminate the double blocking effect, but exposes the gate chamber, as well as service and maintenance personnel that access the closed valve body, to potentially corrosive fluids. Due to the aforementioned advantages and disadvantages in upstream sealing valve seats and downstream sealing valve seats, selection of the appropriate gate valve (i.e., a gate valve with an upstream sealing valve seat or a downstream sealing valve seat) will depend on the particular application and type of fluid that will be flowing through the valve. However, in some cases, conditions and/or the fluid flowing through the valve may change, and the gate valve initially selected and installed is no longer ideal.
In many conventional gate valves, the valve seat forms a planar metal-to-metal axial seal with the valve body. However, with such planar axial seals, debris in the fluid flowing through the valve can get trapped between the sealing surfaces and repeatedly pressed between the sealing surfaces as the valve is periodically opened and closed. Overtime, such debris may abrasively wear the sealing surfaces and compromise their ability to effectively sealingly engage.
Accordingly, there remains a need in the art for improved gate valves. Such gate valves would be particularly well received if they provided enhanced durability, could be configured, in the field, to include upstream sealing valve seats or downstream sealing valve seats, and reduced the risk of maintenance and service personnel being exposed to corrosive fluid within the valve.